Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended						3 Months Ended		12 Months Ended
	Mar. 31, 2017	Feb. 28, 2017	Jan. 31, 2017	Sep. 30, 2016	Aug. 31, 2016	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Regulatory liability current	$ 85						$ 85		$ 95
Accrued rate refunds	73						73		21
Revenue							1,829	$ 1,801
Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current	85						85		95
Accrued rate refunds	73						73		21
Revenue							1,737	$ 1,723
2016 Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested						$ 225
Rate of return on equity requested						10.70%
Annual rate increase self-implemented				$ 170
Annual rate increase authorized		$ 113
Rate of return on equity authorized		10.10%
2016 Electric Rate Case [Member] | Revenue Subject To Refund [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current	16						16
Gas Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested					$ 90
Amended Annual Rate Increase Request	80
Rate of return on equity requested					10.60%
Investment recovery, 2018					$ 35
Investment recovery, 2019					$ 35
Annual rate increase self-implemented			$ 20
Gas Rate Case [Member] | Consumers Energy Company [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase self-implemented			$ 20
Energy Optimization [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection	18						$ 18
Revenue									$ 18
Depreciation Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ (3)
FERC Transmission Order [Member] | Consumers Energy Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Rate of return on equity authorized				10.32%	12.38%
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Accrued rate refunds		$ 28